This invention concerns high-dielectric colorless or virtually colorless dopants for low-voltage and tunable clearing temperature liquid-crystal devices.
A few high dielectric anisotropy compounds have been reported in the literature.
For example, Wu et al., Asia Display, pp. 567-70 (1995) discloses nitro-amino azobenzenes and tolanes with the following structures: 
In another example, Kippelen et al., Science 279, 54 (1998) discloses bicyano-amino polyene dyes with the following structure: 
A general problem with the compounds and dyes disclosed by Wu et al. and Kippelen et al. is that their absorption is too large in the visible region. As a result, their light transmission is greatly reduced. This is particularly undesirable for some displays and electro-optic modulators where high transmittance is required.